In the early hours of May 31, a slurry of mud, trees and boulders - one at least 14 feet across - roared down the middle fork of the Nooksack River.
Called a debris flow by scientists, it would have felt and sounded like a freight train as it rumbled down the river valley for more than 3 miles. Anyone in its path would have been unable to outrun the mass that, at one point, was an estimated 30 feet deep and 150 feet wide. It had the consistency of wet cement.
"If you are in that stream channel and one of these things came down, you're toast," said Dave Tucker, a Bellingham geologist who has visited the flow site numerous times and is director of the Mount Baker Volcano Research Center.
"To be on a trail beside one of these is sensory overload," added Carolyn Driedger, a hydrologist who studies debris flows and has seen them. "If you can, imagine boulders knocking together constantly."
Two other smaller flows have happened since that first big one recorded at 2:54 a.m. May 31, raising ongoing concerns about unstable ground - including boulders, rocks slickened by mud and muddy floods - in an area visited by hikers, picnickers and others.
That's because the Ridley Creek and Elbow Lake trails cross the middle fork in the debris flow area in Mount Baker-Snoqualmie National Forest. Floods washed out the bridges on those trails in 2003, so hikers have had to ford the river since then.
Elbow Lake is a popular fishing area, and both trails are used to access the Mount Baker National Recreation Area.
The river will continue to move the material, and officials are asking people to stay away. Warning signs have gone up in the area at Elbow Lake and Ridley Creek.
There have been no reported injuries as of Friday, June 14, and officials want it to stay that way.
"We could have more debris flows," Driedger said, expressing concerns about visitors to the area. "If they feel this approaching rumble and roar, then get to higher ground" off the valley floor.
People can't outrun debris flows as they usually move at speeds of 20 mph or faster, said Driedger, who is with the U.S. Geological Survey Cascades Volcano Observatory in Vancouver, Wash.
Scientists studying the initial debris flow and two others, on June 1 and 6, stress that the danger is to those in the Ridley Creek and Elbow Lake trail areas, adding there isn't a risk to those living farther downstream. The closest residents are more than 15 miles downstream, they said.
What roiled the Nooksack River began on the Deming Glacier on the west bank of Mount Baker, specifically in an older glacial deposit known as a moraine - consisting of clay, sand and boulders - that existed when the glacier was larger.
"It's material that was carried by the ice and deposited," Tucker explained. "It forms a big, steep wall."
There, at the 4,600-foot-level, a large landslide started and then fell several hundred feet into the river, turning into a slurry of mud with big boulders in it. As it continued rolling down the river, the mass picked up more water and more sediment.
"This is a very big, deep one. This is certainly the biggest that I've seen," said Chris Magirl, a research hydrologist who studies debris flows and has been to the site. He is with the USGS in Tacoma.
And while debris flows are dramatic - Magirl said the first large one must have looked like "chaos" - they are not unusual in the Cascades, including at Mount Rainier and Mount Hood as well as Mount Baker and nearby Glacier Peak.
"This is not new or mysterious phenomena," Driedger said.
In fact, debris flows are sporadic events that occur in the valleys of glaciated volcanoes, such as Mount Baker, because of the abundance of loose volcanic rock, excess water, steep slopes and confining valley walls.
Driedger said the pineapple express storm in November 2006 likely caused debris flows in the same area now under study in the middle fork of the Nooksack.
Beyond safety, these debris flows could harm fish - specifically spawning steelhead in the Nooksack.
Others in the future could have implications for water quantity and quality for cities and agencies that draw their water from the middle fork of the Nooksack, including Bellingham and Lynden.
Scientists from multiple agencies are monitoring the affected area, including from Mount Baker-Snoqualmie National Forest, the Nooksack Tribe, Whatcom County, U.S. Geological Survey, National Weather Service, Western Washington University, and Mount Baker Volcano Research Center.
Scientists said people might see murky water in the middle fork as the river moves loose debris downstream in the coming years. And, they said, the river channel could be reworked for years as the Nooksack moves and redistributes rocks, changing how the area looks.
And those visitors who insist on going to the Ridley Creek and Elbow Lake trail areas also will see changes.
"They're going to find a very different landscape," Driedger said. "It's going to be like Alice in Wonderland."
Go to mbvrc.wordpress.com and type "debris flows" into the search window.
Reach Kie Relyea at 360-715-2234 or firstname.lastname@example.org.